This invention relates to an optical scanner directing a scanned beam through a window into a field of view and, more particularly, to an optical scanner employing two wedge mirrors independently rotatable about an optical axis to provide a desired configuration of scan.
Various forms of optical scanning systems have been employed for scanning a beam of light for illuminating a subject with light produced by a source of light or for detecting light emitted or reflected from the subject to a detector. The term "light" as used herein is to be understood to include visible radiation as well as radiation falling on other portions of the electromagnetic spectrum such as infrared radiation and ultraviolet radiation. Such scanning systems may employ a variety of mirrors and/or other optical elements such as lenses and prisms for producing a raster scan or a spiral scan, by way of example. Scanning is accomplished by movement of mirrors and/or other ones of the optical elements, typically by a pivoting or rotation of the optical elements. For example, in prior art raster mirror scanning, such a scanner might include bidirectional rotation of gimballed flat mirrors. Alternatively, such scanning systems may comprise either single or dual axes, continuous rotation polygons with tilted mirror facets, and single axes wedge mirror rotation in which platform motion, typically in airborne and in space applications, provides the orthogonal axis scanning motion.
A problem exists in that the previously available scanners were overly complex in terms of the mechanisms required to move the various optical elements. Refractive optical elements in the scanner have limited a field of regard (FOR) of the scanner to a circular cone with a half-cone angle less than approximately 70 degrees, and have introduced other disadvantages such as chromatic aberration and image field distortion as a function of beam pointing angle. Where refractive wedge shaped optical elements have been employed in a scanner, the line of sight (LOS) pointing angle was a non-linear function of wedge angle, as well as a non-linear function of radiation wavelength, index of refraction of the optical material, and angle of incidence. Also, the LOS pointing angle has been sensitive to changes in the index of refraction of the material of the refractive optical elements. To achieve a minimum exit window size for an internally mounted two axis gimballed scanning sensor looking through a flush mounted, conformal window, the whole gimballed sensor must be translated or tilted in two axes.